Dialysis machine and method for determining the furring in a dialysis machine

ABSTRACT

The present invention relates to a dialysis machine comprising at least one filter for the filtration of the dialysis liquid and comprising means for determining the calcification of the dialysis machine, wherein the means for the determining of the calcification of the dialysis machine comprising one or more sensors, with the sensor or sensors being configured and arranged such that the ion concentration or a parameter representative of the ion concentration or of its change of the dialysis liquid, of a solution serving the decalcification or of another measuring solution can be detected by these either downstream or upstream and downstream of the at least one filter, and wherein the means for determining the calcification of the dialysis machine furthermore have an evaluation or calculation unit which is configured such that it determines the calcification of the dialysis machine on the basis of the ion concentration or parameter value detected by means of the sensor or sensors. The invention further relates to a method of determining the calcification of a dialysis machine.

The present invention relates to a dialysis machine comprising at least one filter for the filtration of the dialysis liquid and comprising means for determining the calcification of the dialysis machine. The invention further relates to a method of determining the calcification of a dialysis machine.

In the use of dialysis liquids which simultaneously contain high concentrations of calcium ions (Ca²⁺) and bicarbonate ions (HCO₃ ⁻), the precipitation of lime (CaCO₃) can occur and lime deposits can result in the dialysis machine as a consequence thereof. Under extreme conditions such as, for example, with an additionally low acid content, with long dialysis times or for the case that no decalcifying disinfection is carried out between two dialysis treatments, the said lime deposits can result in failure of the production of dialysis liquid, for example, by blocking of the conveying pumps or by calcification of dialysis liquid filters.

A dialysis machine is known from EP 0 834 328 A1 which comprises means via which an automatic decalcification of the dialysis liquid circuit of the machine can be initiated on the finding of a predetermined degree of calcification of the dialysis machine. Provision can be made in this process for the degree of calcification of the dialysis machine to be able to be determined by clouding of a window of a blood leak detector or by the determination of characteristic parameters of the conveying pump for the dialysis liquid. On the presence of criteria for a decalcification, provision can furthermore be made for the dialysis machine to initiate a decalcification cycle in a fully automatic process.

Whereas the problem of calcification at the machine side, which can result in an abortion of the dialysis and thus in a non-achievement of the treatment goal, is thus generally known, the effects of the lime deposition in the machine on the calcium supply to the patient have previously only been rarely looked at. It is evident that the calcium deposited in the dialysis machine, which is precipitated in the form of lime, can no longer reach the patient. It has been able to be shown in laboratory measurements that the precipitation of CaCO₃ can lower the Ca²⁺ ion content at the dialysis-side inlet of the dialyzer to less than 50% of the prescription. This lowering takes place much faster than the failure of the machine due to calcification under specific conditions.

The case can thus occur that the patient is treated with a dialysis liquid for a fairly long time whose Ca²⁺-ion concentration is below the concentration of the ionized calcium in the plasma, which can have the consequence that calcium is removed from the patient in an unwanted manner in the dialysis treatment. The ionized Ca is of great significance with respect to nervous conduction, muscular contraction, myocardial contraction and blood pressure. It can therefore be imagined that negative effects on the patient can occur as a consequence of the machine calcification.

It is the underlying object of the present invention to further develop a dialysis machine of the initially named kind such that the calcification of the dialysis machine can be recognized reliably before the calcification results in the abortion of the treatment and before the patient is treated with concentrations of calcium ions which are too low over a fairly long period.

This object is satisfied by a dialysis machine having the features of claim 1. Provision is accordingly made for the machine to have means for determining the calcification of the dialysis machine which comprise one or more sensors, with the sensor or sensors being configured and arranged such that the ion concentration or a parameter of the dialysis liquid representative of the ion concentration or of its change, of a solution serving the decalcification or another measuring solution can be detected upstream or downstream of the filter. The means for determining the calcification of the dialysis machine furthermore comprise an evaluation or calculation unit which is configured such that it determines the calcification of the dialysis machine on the basis of the ion concentration or parameter value detected by means of the sensor or sensors.

The sensor or sensors can, for example, be conductivity sensors, ion-selective electrodes, pH electrodes or sensors working in accordance with spectroscopic processes.

The underlying idea of the invention is that the ion concentration, preferably the Ca²⁺ concentration, or a parameter representative of the ion concentration or of its change, such as the conductivity, are preferably detected downstream, or also upstream and downstream, of the filter or filters and that a conclusion can be made on the calcification of the filter on this basis. In this connection, the ion concentration or the said parameter of the dialysis liquid, of a solution provided for decalcification or of another solution can be detected. This other solution can be an ion-containing solution which, for example, contains Ca²⁺ or H⁺ ions. Provision can be made in this connection for two sensors to be associated with at least one of the filters, of which one is arranged upstream of the filter and another downstream of the filter. It is conceivable to make the monitoring of the filter or the determination of the degree of calcification of the filter by a comparison of two conductivity measured values, of which one is recorded directly before the filter to be checked and one after the filter to be checked. A calcification of the filter is present when the conductivity value measured upstream of the filter is larger than the conductivity value measured downstream of the filter.

The term of the detection of the “ion concentration of a parameter representative of the ion concentration or of its change” is to be interpreted broadly and comprises, inter alia, also indirect measuring methods for the ion measurement. The measurement of CO₂, which is created in the decalcification is, for example, conceivable and covered by the invention. The CO₂ concentration is related via the chemical balance to the concentration of other ions and thus forms a measure for the ion concentration so that the measurement of, for example, the CO₂ amount, the CO₂ concentration or the CO₂ volume represents an embodiment of the detection of a parameter representative of the ion concentration.

It is conceivable that a respective sensor is associated upstream and downstream with at least one of the filters both on the primary side of the filter and on the secondary side of the filter. This arrangement makes it possible to detect the calcification of the filter both on the primary side and on the secondary side.

In a further aspect of the invention, provision is made for at least one bypass line to be arranged which can be cut off and which, in the open state, establishes a flow communication of two sensors while bypassing at least one of the filters. If the influence of the filter on the measured values obtained by means of the sensors should be precluded, they are connected to one another in such a manner while bypassing the filter that the dialysis liquid serving the decalcification or a measuring solution first flows through the one and then the other sensor. This makes it possible to be able to compare the measurement values of the sensor with one another or to be able to carry out a calibration of the sensors.

Provision is made in a further aspect of the invention for only one sensor to be provided per filter or for a plurality of filters and for it to be arranged downstream of the filter or filters. A monitoring of the calcification of the filter is thus also possible using one sensor, for example using a conductivity measuring cell which is located downstream of the filter. A determination of the calcification can now take place, for example, in that the conductivity measured value is determined before the start or at the start of the treatment and a check is made during the treatment or also after the treatment as to whether and to what extent a measured value change has occurred.

It is particularly advantageous for at least one bypass line to be provided which can be cut off and which is arranged such that, in the open state, it supplies the dialysis liquid, the solution serving the decalcification or the other measuring solution to the sensor while bypassing at least one filter. It is thus possible also to determine the ion concentration or the parameter representative of this or of its change upstream and downstream of the filter using only one sensor, for example using a conductivity measuring cell arranged downstream of the filter. If the ion concentration or said parameter should be detected upstream of the filter, the bypass line is opened and the solution extracted upstream of the filter by means of the bypass line is supplied to the sensor. The bypass line is closed and the filter is accordingly flowed through for the detection of the measured value on the flowing through of the filter. It is an advantage of this process that only one sensor per filter is needed or also only one sensor is needed for a plurality of filters with associated electronics. In addition, a calibration of a plurality of sensors relative to one another is dispensed with.

The invention furthermore relates to a method of determining the calcification of a dialysis machine, in particular of a dialysis machine in accordance with one of the claims 1 to 8, with the dialysis machine comprising at least one filter for the filtration of the dialysis liquid.

The method is characterized in that the ion concentration or a parameter representative of the ion concentration or of its change of the dialysis liquid or of a solution serving the decalcification or a measuring solution is measured either downstream or upstream and downstream of the filter for the determination of the calcification of the dialysis machine and in that the calcification is determined on the basis of the ion concentration or of the parameter value of the calcification measured. As stated above, the parameter representative of the ion concentration can, for example, be the conductivity, the pH or a parameter determined by means of an ion-selective electrode or by means of spectroscopic processes, such as the absorption or the transmission, for example. The ion concentration is preferably the Ca²⁺ ion concentration or the H⁺ ion concentration.

Two sensors can be associated with the at least one filter and are arranged downstream and upstream of the filter. The degree of calcification can be determined by a comparison of the ion concentration or of the parameter representative for it or for its change measured upstream and downstream. Provision can be made in this connection for differences in the measured values of the sensors to be determined at a first point in time, preferably before or at the start of a treatment and for these differences then to be taken into account in the determination of the degree of calcification at a second point in time after the first point in time, in particular during the treatment. It is also feasible that the said measured value differences are eliminated by corresponding calibration of the sensors.

In a further aspect of the invention, provision is made for at least one bypass line which can be cut off to be provided which, in the open state, establishes a connection of two sensors while bypassing one of the filters and for the bypass line to be opened for the purpose of determining measured value differences or for calibration of the sensors.

Only one sensor can also be provided per filter or for a plurality of filters and is arranged downstream of the filter or filters, with a measured value being determined at a first point in time, preferably before or at the start of a treatment, by means of the sensor and a check can be made at a second point in time, disposed after the first point in time, in particular during the treatment, whether a measured value change has occurred.

It is also conceivable that only one sensor is provided per filter or for a plurality of filters and is arranged downstream of the filter or filters and that at least one bypass line is provided which can be cut off and which is arranged such that, in the open state, it supplies the dialysis liquid, the solution serving the decalcification or the other measuring solution to the sensor while bypassing at least one filter, with the measured value of the sensor being determined with an open bypass line at the start of or during the treatment and this measured value being compared with the measured value obtained after the flowing through of the filter.

Provision is made in a further aspect of the invention for a decalcification to be carried out and for an evaluation of the decalcification to be carried out after or during the decalcification, said evaluation being based on a comparison of measured values of the one sensor or of the several sensors by means of which the ion concentration or the parameter representative of the ion concentration or of its change is detected upstream and downstream of the filter.

Provision can furthermore be made for an evaluation of the decalcification to be made after the decalcification, said evaluation being based on a comparison of measured values of a sensor before and after the decalcification, with the sensor being arranged downstream of the filter or filters and being configured such that the ion concentration or the parameter representative of it or of its change being detected therewith.

The ion concentration can, for example, be the Ca²⁺ ion concentration or also the H⁺ ion concentration.

Further details and advantages of the invention will be explained in more detail with reference to an embodiment shown in the drawing. There are shown:

FIG. 1: time curve of the conductivity on Ca precipitation with still dialysis liquid with contact to the atmosphere;

FIG. 2: flow plan of a dialyzer with online preparation of the dialysis liquid;

FIG. 3: time curve of the Ca²⁺ ion concentration and of the conductivity during a dialysis treatment with fresh dialysis liquid before and after decalcification;

FIG. 4: time curve of the Ca²⁺ ion concentration and of the conductivity on the installation and removal of calcified filters;

FIG. 5: schematic representation of the calcification monitoring with two conductivity measuring cells per filter;

FIG. 6: schematic representation of the calcification monitoring with two conductivity measuring cells per filter, and bypass circuit;

FIG. 7: schematic representation of the calcification monitoring with only one conductivity measuring cell per filter and bypass circuit;

FIG. 8: flow plan of the dialyzer in accordance with FIG. 2 with calcification monitoring of all filters by additional conductivity measuring cells;

FIG. 9: flow plan of the dialyzer in accordance with FIG. 2 with calcification monitoring of all filters by additional conductivity measuring cells with a calibration possibility; and

FIG. 10: flow plan of the dialyzer in accordance with FIG. 2 with calcification monitoring of all filters by a conductivity measuring cell and bypass circuits.

The conductivity of the dialysis liquid is determined by its individual components. The main contribution of the conductivity is due to NaCl, but the Ca²⁺ ions present in relatively low concentrations also contribute to the conductivity. If a dialysis liquid containing both Ca²⁺ and HCO₃ ⁻ is in contact with the atmosphere, the outgasing of CO₂ results in a consumption of hydrogen carbonate and thus in a pH value shift into the alkaline, which in turn effects a precipitation of calcium carbonate. This is illustrated by the following reaction equation:

Ca²⁺+2HCO₃ ⁻→CaCO₃↓+CO₂ ↑+H₂O

Ions are thus stripped from the dialysis liquid so that the conductivity of the solutions falls. This was able to be demonstrated in lab trials. FIG. 1 shows the drop in conductivity over time with a still dialysis liquid with contact to the atmosphere. As is clearly visible from FIG. 1, the conductivity of the solution falls over time. As can further be seen from the measured values set forth in FIG. 1, this is essentially due to the reduction in the content of calcium ions and, parallel to this, the consumption of hydrogen carbonate ions.

A quantifying of the change in the Ca²⁺ ion concentrations in the dialysis liquid is also possible via the change in the conductivity.

Empirical investigations of the influence of the Ca²⁺ ion concentration on the conductivity in typical dialysis liquids produced the following connection:

${\Delta \; c} = {\left( {110\; \frac{{\mu S}\text{/}{cm}}{{mmol}\text{/}l}} \right)^{- 1}\Delta \; {LF}}$

With a measuring precision for the conductivity of 10 μS/cm, changes in the Ca²⁺ ion concentration can thus be quantified with an accuracy of 0.1 mmol/l by precipitation of CaCO₃.

If, in contrast, the dialysis liquid is generated continuously as fresh using a dialyzer by mixing RO water with an acid component and a bicarbonate containing component, no precipitation is initially to be expected within the short time between the generation and the transport to the dialysis machine.

For the further illustration of the problems of precipitation of CaCO₃, reference is initially made to FIG. 2. This Figure shows a flow plan of a dialyzer with online preparation of the dialysate from RO water, acid and bicarbonate. As can be seen from FIG. 2, two sterile filters D1 and D2 are arranged upstream of the dialysis machine D3. In this connection, the sterile filters D1 and D2 are arranged such that the dialysis liquid reaching the dialysis machine D3 moves from the primary side to the secondary side of the first sterile filter D1 and then flows through the primary side of the second sterile filter D2. Substituate is gained in this which is added to the blood of the patient as required, as is the case with hemofiltration and hemodiafiltration. The present invention is naturally not restricted to hemodiafiltration or hemofiltration, but also includes the process of hemodialysis inter alia.

As can further be seen from FIG. 2, a conductivity measuring cell 20 is arranged upstream of the second sterile filter D2 and a second conductivity measuring cell 40 is arranged downstream of the dialysis machine D3 and of the first sterile filter D1.

The conductivity of the dialysis liquid was measured continuously by means of the conductivity of the measuring cell 20.

In addition, the Na⁺ and Ca²⁺ ion concentration was determined in samples of the dialysis liquid taken directly downstream of the dialysis machine D3.

In FIG. 3, the conductivity measured values (solid line) and the measured values of the Ca ion concentration (circles) are set forth. With a dialysate with a high Ca²⁺ and HCO₃ ⁻ content, a clear drop in the Ca²⁺ ion concentration and in the conductivity of the dialysis solution resulted after approximately 2 hours. After intense flushing with a decalcifying cleaning agent, peracetic acid for example, the original Ca²⁺ ion concentrations were again measured, as can be seen from FIG. 3. The conductivity likewise increased again, but with effects by cell drift over time as well as a potential effect of the calcification of the conductivity measuring cell itself having to be taken into account. The Na⁺ ion concentration remained constant in all cases so that changes in the mixture relationship in the generation of the dialysis liquid can be precluded.

The process shown in FIG. 3 of the drop in conductivity and in the calcium ion concentration can be explained in that the dialysis liquid is oversaturated at a high Ca²⁺ ion concentration and HCO₃ ⁻ concentration so that the presence of crystallization nuclei, rough surfaces or pressure fluctuations due to the conveying of the dialysis liquid by means of the conveying pump results in the spontaneous precipitation of CaCO₃.

It was furthermore now possible to show in laboratory trials that in particular the dialysis liquid filters D1 and D2 are not only the preferred sites for calcification, but also promote the further precipitation themselves on starting calcification:

To verify this, the dialysis liquid filters D1 and D2 were installed and removed on a dialyzer in running operation in accordance with FIG. 2. The conductivity was measured continuously by means of the conductivity measuring cells 20 and 40. As also described above, the sodium and calcium ion concentrations were additionally determined in dialysate samples taken upstream of the dialysis machine D3.

As can be seen from FIG. 4, the conductivity fell on installation of the filter D1 at both the sensors 20 (LF2) and 40 (LF4) by approximately 60 μS/cm with respect to the conductivity without a filter. At the same time as the change in conductivity, a fall in the Ca²⁺ ion concentration before the dialysis machine D3 by 0.6 mmol/l could also be found on installation filter D1.

If a calcified filter D2 was additionally installed, the conductivity (LF4) at the sensor 40 fell by a further approximate 50 μS/cm and the Ca²⁺ ion concentration by a further 0.4 mmol/l since the flow path to the sensor 40 now contained two calcified filters D1, D2. The conductivity (LF2) at the conductivity 20 remained constant.

After removal of the two filters D1, D2, the conductivity and the Ca²⁺ ion concentration at both measuring cells again reached the original value, as can be seen from FIG. 4.

For clarification, it should be pointed out at this point that the extent of the curve of the value “LF4” in FIG. 4 does not only exist, for instance, in the area “with filters D1 and D2!, but also in the time period before it in which it does not substantially differ from the curve of the parameter “LF2”.

It is furthermore pointed out that the measured curves in accordance with FIG. 3 and FIG. 4 are measurements which were obtained in an in vitro structure, with a comparison liquid being circulated instead of blood in the extracorporeal blood circuit. Favorable and unfavorable compositions for the dialysis liquid exist for the occurrence of calcification, in particular with respect to its content of bicarbonate, calcium and acetate. Such combinations were now selected for the trials in which the calcification tended to proceed fast rather than slow. The data and curves shown are therefore not representative for an average dialysis treatment. The measurements shown are rather extreme situations by means of which the effects playing a role within the framework of this invention can be illustrated better.

The values of the Ca²⁺ ion concentration are in good approximation with the change in the Ca²⁺ ion concentration calculated in accordance with the above equation from the change in conductivity. The Na⁺ ion concentration remained constant in all cases so that changes in the mixture relationship in the generation of the dialysis liquid can be precluded.

The recognition of calcification in the embodiment shown here is based on a change in the conductivity with a mixing ratio which remains constant on the generation of the dialysis liquid, with the change in the conductivity being due to the precipitation of the calcium in the form of calcium carbonate. It must therefore be ensured that both the metering system and the conductivity measurement are not subject to any drifts over the duration of the comparison measurements.

The laboratory experiments were only carried out with compositions of the dialysis liquid which resulted in an oversaturation with CaCO₃.

In an aspect of the invention, an apparatus for the recognition of the calcification of the dialysis liquid filter in the dialyzer or the dialysis machine consists of two conductivity measuring cells which are arranged such that the conductivity of the dialysis liquid or also of a solution serving the decalcification or another measuring solution is measured before and after passage through the filter or the dialysis machine. Such an aspect of the invention is shown in FIG. 5, with the conductivity measuring cells being shown with the reference numerals 1, 2 and the filter with the reference symbol D.

The conductivity measuring cells 1, 2 must be calibrated to one another beforehand. If the influence of the filter D is to be reliably precluded, a bypass 100 must be provided which surrounds the filter D, as can be seen from FIG. 6. The bypass line 100 can be cut off by a valve. The line leading to the filter D can equally be cut off by a valve. Accordingly, depending on the switching of the valves shown in FIG. 6, either the filter D or the bypass line 100 can be flowed through. If a calibration of the conductivity measuring cells 1, 2 should be carried out, the bypass line 100 is flowed through; if the calcification of the filter D should be determined, the bypass line 100 is closed, the filter is flowed through and it is determined by means of the conductivity measuring cells 1, 2 whether a difference can be found in the conductivity values determined upstream and downstream of the filter D.

It is also possible alternatively to this to carry out the monitoring of the calcification by only one conductivity measuring cell which is shown with the reference numeral 2 in FIG. 7. This measuring cell is located downstream of the filter D. Furthermore, a bypass line 200 is provided which surrounds the filter D. As can be seen from FIG. 7, the bypass line 200 can likewise be cut off by a valve. The same applies to the line leading to the filter D. If the ion concentration or a parameter representative of this should be determined upstream of the filter D, the bypass line 200 is opened and the conductivity value is detected by means of the conductivity measuring cell 2. If the conductivity should be detected after flowing through the filter D, the line leading to the filter D is opened and the bypass line 200 is closed.

The arrangement in accordance with FIG. 7 provides the advantage that only one conductivity measuring cell with associated electronics is required and, additionally, a calibration of a plurality of measuring cells can also be dispensed with. It must be mentioned as a disadvantage that stabilization times occur here on the switching of the flow paths to measure the conductivity. Furthermore, fairly long times arise in which no dialysis may be possible if the flowing through of the filter D is required for the treatment of the patient.

FIG. 8 shows the flow scheme in accordance with FIG. 2 with an arrangement of conductivity measuring cells according to the principle described in FIG. 5. The conductivity measuring cells 10, 20 serve the calcification monitoring of the sterile filter D1 and the measuring cells 10, 40 serve the calcification monitoring of the primary side of the sterile filter D1. The conductivity measuring cells 20, 30 serve the monitoring of the sterile filter D2 and the measuring cells 30, 40 serve the monitoring of the dialysis machine D3.

A flow plan in accordance with FIG. 9 results with a simultaneous calibration possibility in accordance with the principle described in FIG. 6. As can be seen from FIG. 9, bypass lines 100 are respectively provided which are arranged such that each of the conductivity measuring cells 10, 20, 30 can be connected in series with the conductivity measuring cell 40. Accordingly, the calibration of the conductivity measuring cells takes place here by corresponding valve circuits in that the conductivity measuring cells 10, 20 and 30 are connected in series with the conductivity measuring cell 40 while bypassing the respectively subsequently disposed filter D1, D2, D3. This calibration is possible before the start of the dialysis. The valves are switched during the dialysis so that the flow plan in accordance with FIG. 8 results.

As can furthermore be seen from FIG. 10, a monitoring of all filters D1, D2, D3 is also possible with only one conductivity measuring cell 40 by the introduction of bypass lines 200.

The conductivity measuring cell 40 is arranged downstream of the filters D1, D2 and of the dialysis machine D3. For a reference measurement, the bypass lines 200 with the valves V3, V6 and V7 are opened and the valves V2, V5 and V8 in the feed lines to the filters D1, D3 as well as the dialysis machine D3 are closed so that the dialysis liquid flows around the filters D1, D2 and the dialysis machine D3 in the bypass. The valves V10 and V9 are likewise closed.

If the filter D1 should be checked for calcification, the valves V2, V6 and V7 are opened so that the dialysis liquid only flows through the filter D1 from the primary side to the secondary side, whereas a bypass around the filter D2 and the dialysis machine D3 takes place with open valves V6 and V7. All other valves are closed in this case.

If a check of the sterile filter D1 on the primary side should be carried out, the valves V2 and V10 are opened and all other valves are closed. In this case, the dialysis liquid flows through the valve V2, then through the primary side of the sterile filter D1 and then the valve V10 to finally reach the conductivity measuring cell 40.

A check of the calcification state of the sterile filter D2 takes place by opening the valves V3, V5, V7 and by closing all further valves. A check of the dialysis machine D3 takes place with open valves V3, V6, V8, V9, while all further valves are closed.

The table set forth in the following again summarizes which valves are open and closed for the check of which filter or of the dialysis machine and simultaneously shows which conductivity measuring cell can be replaced by the respective arrangements (reference numerals of FIG. 9).

Replaced conductivity Test Open Closed cell Reference V3, V6, V7 V2, V5, V8, V9, V10 LF1 (10) D1 V2, V6, V7 V3, V5, V8, V9, V10 LF2 (20) D1, primary V2, V10 V3, V5, V6, V7, V8, V9 / side only D2 V3, V5, V7 V2, V6, V8, V9, V10 LF3 (30) D3 V3, V6, V8, V9 V2, V5, V7, V10 /

With these theoretically possible switching possibilities, it was not yet taken into account that certain switchings may be less relevant in practice due to the lack of conductivity sensors prescribed for a dialysis treatment and/or of filter stages for the dialysis liquid.

In accordance with the principle described in FIG. 10, a partial reduction of the number of the conductivity measuring cells shown in FIGS. 8 and 9 is also possible.

The conductivity can now be measured continuously for the continuous monitoring of the machine calcification. For this purpose, drifts in the conductivity measurement must possibly be compensated to be able to recognize changes in the conductivity (not the absolute value of the conductivity) with a precision of 0.01 mS/cm.

The procedure of the continuous monitoring of the machine calcification in an arrangement in accordance with FIG. 9 has the following structure:

After a calibration of all conductivity measuring cells 10, 20, 30, 40, the conductivity is measured continuously with them. The monitoring of the filters D1 and D2 takes place by a comparison of the conductivity respectively measured directly before or after the respective filter. A calcification of the filter is present when the conductivity measured after the filter is less than the conductivity measured before the filter. A conclusion on the degree of calcification can be concluded by means of the equation set forth above in the form of a concentration difference. It is important that sufficiently long stabilization times are waited through on changes to the dialysate composition during the treatment.

An initially already present calcification of the filters can be easily recognized using the method in accordance with the invention.

If the dialysis machine D3 should be monitored, it is necessary to eliminate the influence on the patient by stopping the blood pump. At the same time, the flow of the dialysis liquid should be set as high as possible for the fast stabilization of the conductivity at the conductivity measuring cells 30, 40. The evaluation then takes place as described above as for the filters D1 and D2.

If no calibration of the conductivity measuring cells should be carried out via any bypass lines, as applies to FIG. 8, any measuring differences of the individual conductivity measuring cells 10, 20, 30, 40 must be determined at the start of the treatment without the influence of the patient with stable conductivity. The monitoring is then possible as described above while taking account of these initial measuring differences. However, a calcification already present at the start of the treatment cannot be detected precisely in this manner, which represents a disadvantage with respect to the arrangement in accordance with FIG. 9.

As stated above it is also possible that not two conductivity measuring cells are arranged per filter, but only one conductivity measuring cell. In this connection, the one conductivity measuring cell can also be associated with a plurality of filters, as is shown in FIG. 10. In this connection, for each of the filters D1, D2 to be monitored, a measuring cell in accordance with FIG. 7 or FIG. 10 disposed downstream of this filter is required. If no bypasses bypassing the filter should be provided, as is the case, for example, in FIG. 7, and if the composition of the dialysis solution remains constant during the total treatment, an initial value of the conductivity LF₀ is determined and stored at the start of the treatment. A fall in the conductivity measured continuously in the further course with respect to the value LF₀ then indicates an increase in calcification.

A calcification already present at the start cannot be recognized in this manner.

If the composition of the dialysis liquid changes during the treatment, if the desired sodium value is adjusted by the user during the treatment, for example, then an expected value for the conductivity change can be calculated by means of an empirically determined formula on the basis of the concentration composition and on the conductivity measured at the start. If the measured conductivity falls below the expected conductivity, this is an indication of calcification.

If the filters should each be fitted with bypasses, the full extent of a continuous calcification monitoring and an initial calcification monitoring of all filters can be achieved as described above.

The cause of the presence of calcified filters can be found, for example, in the fact of an insufficient decalcification between treatments. Other causes are the use of already calcified filters or the multiple use of dialysis machines. As stated above, in this connection, there is the risk of the failure of the dialyzer due to lime deposits and, in some cases, the endangering of the patient due to a Ca²⁺ ion concentration of the dialysis liquid which is too low.

As stated above, the calcification recognition can consist of a concentrate mixture being set such that an oversaturated solution is present and that then the conductivity measured values are recorded upstream and downstream of the filter and/or of the dialysis machine to be checked. If bypass circuits are used, a sufficiently long stabilization time must be observed in each case. If the conductivity measured downstream is less than the conductivity measured upstream, calcification can be concluded, with its degree being able to be determined via the aforesaid equation.

If the decalcification process itself should be monitored, the measurement of the conductivity can take place before and after the carrying out of the decalcification cycle or also during the decalcification.

The degree of the calcification can be determined for the filter to be monitored by the method described above (measurement of the conductivity upstream and downstream of the filter) before carrying out the decalcification procedure. After carrying out the decalcification, a renewed determination of the conductivity takes place upstream and downstream of the filter. The filter is completely decalcified when the conductivity upstream and downstream of the filter is identical.

An evaluation of the decalcification is also possible when only one conductivity measuring cell is arranged downstream of the filter. This applies, for example, to the filter D1 and to the conductivity measuring cell 20 in FIG. 2. To carry out the evaluation of the decalcification here, a concentrate mixture may have to be set such that an oversaturated solution is present. Then the measurement of the conductivity is carried out by means of the conductivity measuring cell located downstream and then the decalcification procedure is carried out. Subsequently, the said concentration mixture is again established, the stabilization of the conductivity waited for and the conductivity measured value measured again by means of the downstream measuring cell. A decalcification was at least partly successful when the conductivity after the decalcification is larger than that before the calcification. A conclusion on the degree of the elimination of the calcification can be made by means of the aforesaid equation. This process can be repeated so often until the conductivity before and after the decalcification no longer changes.

It is also possible to assess the progress of decalcification during the decalcification. This procedure is based on the fact that the specific conductivity of H⁺ ions exceeds that of the others in the dialysis liquid or in the acid used for the decalcification by four to five fold. On the decalcification of a filter by acid, CaCO₃ goes into solution while consuming H⁺ ions, as is shown by the reaction equation given in the following:

CaCO₃+H⁺→Ca²⁺+HCO₃ ⁻

The process of the decalcification can now be monitored by a comparison of the conductivity before and after the filter by an arrangement in accordance with FIG. 6, for example: The acid solution before the filter has a higher conductivity than that after the filter due to the high H⁺ ion concentration when a consumption of H⁺ ions has occurred by reaction with CaCO₃. The decalcification is ended exactly when the conductivity upstream and downstream of the filter is identical.

A measurement of the conductivity of the dialysate before and after the decalcification is necessary with this process. Alternatively to this, the monitoring can also be carried out by pH sensors during decalcification. As stated above, a consumption of H⁺ ions takes place during the decalcification and thus a shift of the environment into the alkaline. If the pH no longer changes, the decalcification is ended since then a consumption of the H⁺ ions by CaCO₃ no longer takes place. 

1. A dialysis machine comprising at least one filter (D, D1, D2) for the filtration of the dialysis liquid and comprising means for determining the calcification of the dialysis machine, characterized in that the means for the determining of the calcification of the dialysis machine comprise one or more sensors (1, 2, 10, 20, 30, 40), with the sensor or sensors (1, 2, 10, 20, 30, 40) being configured and arranged such that the ion concentration or a parameter of the dialysis liquid representative of the ion concentration or of its change, of a solution serving the decalcification or of another measuring solution can be detected either downstream or upstream and downstream of the at least one filter (D, D1, D2); and in that the means for determining the calcification of the dialysis machine furthermore comprise an evaluation or calculation unit which is configured such that it determines the calcification of the dialysis machine on the basis of the ion concentration or parameter value detected by means of the sensor or sensors (1, 2, 10, 20, 30, 40).
 2. A dialysis machine in accordance with claim 1, characterized in that the sensor or sensors (1, 2, 10, 20, 30, 40) are conductivity sensors, ion-selective electrodes, pH electrodes or sensors working according to spectroscopic processes.
 3. A dialysis machine in accordance with claim 1, characterized in that the ion concentration is the Ca²⁺ ion concentration or the H⁺ ion concentration.
 4. A dialysis machine in accordance with claim 1, characterized in that two sensors (1, 2, 10, 20, 30, 40) are associated with at least one of the filters (D, D1, D2), of which one is arranged upstream and one downstream of the filter (D, D1, D2).
 5. A dialysis machine in accordance with claim 1, characterized in that one respective sensor (10, 20, 40) is associated with at least one of the filters (D1) both on the primary side and on the secondary side of the filter (D1) upstream and downstream.
 6. A dialysis machine in accordance with claim 1, characterized in that at least one bypass line (100) is provided which can be cut off and which is arranged such that, in the open state of the bypass line (100), the dialysis liquid, the solution serving the decalcification or the measuring solution is guided by a sensor (1, 10, 20, 30) while bypassing at least one of the filters (D, D1, D2) to another sensor (2, 40).
 7. A dialysis machine in accordance with claim 1, characterized in that only one sensor (2, 40) is provided per filter (D, D1, D2) or for a plurality of filters (D1, D2) and is arranged downstream of the filter or filters (D, D1, D2).
 8. A dialysis machine in accordance with claim 7, characterized in that at least one bypass line (200) is provided which can be cut off and is arranged such that, in the open state, the dialysis liquid, the solution serving the decalcification or the measuring solution is supplied to the sensor (2, 40) while bypassing at least one filter (D, D1, D2).
 9. A method of determining the calcification of a dialysis machine, in particular of a dialysis machine in accordance with claim 1, which comprises at least one filter (D, D1, D2) for the filtration of the dialysis liquid, characterized in that the ion concentration or a parameter representative of the ion concentration or of its change of the dialysis liquid, of a solution serving the decalcification or of another measuring solution is measured either downstream or upstream and downstream of the filter (D, D1, D2) for the determining of the calcification of the dialysis machine; and in that the calcification of the dialysis machine is determined on the basis of the ion concentration or the parameter value measured.
 10. A method in accordance with claim 9, characterized in that the parameter representative of the ion concentration is the conductivity, the pH or a parameter determined by means of an ion-selective electrode or of a spectroscopic method.
 11. A method in accordance with claim 9, characterized in that two sensors (1, 2, 10, 20, 30, 40) are associated with at least one of the filters (D, D1, D2), one of which is arranged upstream and one downstream of the filter (D, D1, D2); and in that the calcification of the filter is determined by a comparison of the ion concentration or of the parameter representative of the ion concentration or of its change measured upstream and downstream.
 12. A method in accordance with claim 11, characterized in that differences in the measured values of the sensors (1, 2, 10, 20, 30, 40) are determined at a first point in time, preferably before or at the start of a treatment, and these differences are then taken into account in the determination of the calcification at a second point in time disposed after the first time point, in particular during the treatment.
 13. A method in accordance with claim 9, characterized in that at least one bypass line (100) is provided which can be cut off and which is arranged such that, in the open state of the bypass (100), the dialysis liquid, the solution serving the decalcification or the measuring solution is guided from a sensor (1, 10, 20, 30) to another sensor (2, 40) while bypassing at least one of the filters (D, D1, D2); and in that the bypass line (100) is opened for the purpose of determining measured value differences of the sensors (1, 2, 10, 20, 30, 40) or for the calibration of the sensors (1, 2, 10, 20, 30, 40).
 14. A method in accordance with claim 9, characterized in that only one sensor (40) is provided per filter (D, D1, D2) or for a plurality of filters (D1, D2) and is arranged downstream of the filter or filters (D, D1, D2); and in that a measured value is determined by means of the sensor (2, 40) at a first point in time, preferably before or at the start of a treatment; and in that check is made after a second point in time disposed after the first point in time, in particular during the treatment, whether a measured value change occurs.
 15. A method in accordance with claim 9, characterized in that only one sensor (2, 40) is provided per filter (D, D1, D2) or for a plurality of filters (D1, D2) and is arranged downstream of the filter or filters (D, D1, D2); and in that at least one bypass line (200) is provided which can be cut off and which is arranged such that, in the open state of the bypass line (200), the dialysis liquid, the solution serving the decalcification or another measuring solution is supplied to the sensor (2, 40) while bypassing at least one filter (D, D1, D2), with the measured value of the sensor being determined with an open bypass line and this measured value being compared with the measured value obtained after flowing through the filter (D, D1, D2).
 16. A method in accordance with claim 9, characterized in that a decalcification is carried out; and in that an evaluation of the decalcification is made after the decalcification or during the decalcification which is based on a comparison of measured values of the one or several sensors (1, 2, 10, 20, 30, 40) by means of which the ion concentration or the parameter representative of the ion concentration or of its change is detected upstream and downstream of the filter (D, D1, D2).
 17. A method in accordance with claim 9, characterized in that an evaluation of the decalcification is carried out after the decalcification which is based on a comparison of measured values of a sensor (2, 40) before and after the decalcification, with the sensor (2, 40) being arranged downstream of the filter or filters (D, D1, D2) and being configured such that the ion concentration or the parameter representative of the ion concentration or of its change is detected.
 18. A method in accordance with claim 9, characterized in that the ion concentration is the Ca²⁺ ion concentration or the H⁺ ion concentration. 